Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$41.64	8.783%	$45.2972	$45.30	$45.30	$45.30
Purchase #2	$69.34	3.570%	$71.8154	$71.82	$71.80	$71.80
Purchase #3	$226.85	10.572%	$250.8326	$250.83	$250.85	$250.80
Purchase #4	$128.52	9.617%	$140.8798	$140.88	$140.90	$140.90
Purchase #5	$139.93	10.825%	$155.0774	$155.08	$155.10	$155.10
Purchase #6	$147.81	11.452%	$164.7372	$164.74	$164.75	$164.70
Purchase #7	$233.63	7.767%	$251.776	$251.78	$251.80	$251.80
7 purchase totals =	$987.72		$1,080.4156	$1,080.43	$1,080.50	$1,080.40